build: stop clang complaining about redefined typedefs

Clang's gnu99 mode is not quite the same as GCC's. It will complain
about redefined typedefs being a C11 feature, while GCC does not
complain and allows them in gnu99 mode.
Reviewed-by: NFabiano Fidêncio <fidencio@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

m4/virt-compile-warnings.m4

@@ -125,6 +125,10 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
     # We do "bad" function casts all the time for event callbacks
     wantwarn="$wantwarn -Wno-cast-function-type"
 
+    # CLang incorrectly complains about dup typedefs win gnu99 mode
+    # so use this CLang-specific arg to keep it quiet
+    wantwarn="$wantwarn -Wno-typedef-redefinition"
+
     # GNULIB expects this to be part of -Wc++-compat, but we turn
     # that one off, so we need to manually enable this again
     wantwarn="$wantwarn -Wjump-misses-init"